Facile in situ reductive synthesis of both nitrogen deficient and protonated g-C(3)N(4) nanosheets for the synergistic enhancement of visible-light H(2) evolution

A new strategy is reported here to synthesize both nitrogen deficient and protonated graphitic carbon nitride (g-C(3)N(4)) nanosheets by the conjoint use of NH(4)Cl as a dynamic gas template together with hypophosphorous acid (H(3)PO(2)) as a doping agent. The NH(4)Cl treatment allows for the scalable production of protonated g-C(3)N(4) nanosheets. With the corresponding co-addition of H(3)PO(2), nitrogen vacancies, accompanied by both additional protons and interstitially-doped phosphorus, are introduced into the g-C(3)N(4) framework, and the electronic bandgap of g-C(3)N(4) nanosheets as well as their optical properties and hydrogen-production performance can be precisely tuned by careful adjustment of the H(3)PO(2) treatment. This conjoint approach thereby results in improved visible-light absorption, enhanced charge-carrier separation and a high H(2) evolution rate of 881.7 μmol h(−1) achieved over the H(3)PO(2) doped g-C(3)N(4) nanosheets with a corresponding apparent quantum yield (AQY) of 40.4% (at 420 nm). We illustrate that the synergistic H(3)PO(2) doping modifies the layered g-C(3)N(4) materials by introducing nitrogen vacancies as well as protonating them, leading to significant photocatalytic H(2) evolution enhancements, while the g-C(3)N(4) materials doped with phosphoric acid (H(3)PO(4)) are simply protonated further, revealing the varied doping effects of phosphorus having different (but accessible) valence states.